Colour inkjet printers typically use a four-ink inkset, termed a CYMK set, comprising cyan, yellow, magenta and black inks for printing a spectrum of colours on a media substrate.
Delivering optimal image quality in such inkjet ink sets is challenging, particularly on non-porous media substrates. Grain is a key image quality factor, and can result for many reasons, including isolated and clustered dot visibility, half-toning algorithm and method, printer hardware sources such as media advance and printhead ejection characteristics (drop size, directionality, single or multiple droplets, spray, etc.), and coalescence of ink droplets on the media surface. Coalescence describes wet ink drops touching one another on the surface of the media substrate and is particularly difficult to control on non-porous media. This coalescence artefact, which often occurs in high-speed printing, causes images to appear blotchy or “puddled”, resulting in non-uniformity in solid fill areas, which is generally perceived as grain.